"The Doctors" star Dr. James Sears will be leaving the show under a cloud TMZ has learned ... he's being investigated for allegedly threatening a man's life and it's all over a woman.

According to law enforcement and other sources ... Sears' girlfriend was at his Huntington Beach home near L.A. last month and something happened to make her feel uneasy. She told cops she called her ex-BF Pete Scalisi to pick her up and he obliged.